A conventional asset tracking system often utilizes Radio Frequency (“RF”) tags attached to assets (e.g., a computer, a mobile unit (“MU”), machinery, equipment, etc) to identify, locate or track such assets. One of the major benefits of such an RF tracking system is that a line of sight (“LOS”) between an RF reader or interrogator and the RF tag is not required for communication. This allows a large group of assets to be entered into the RF tracking system without any significant handling.
There are a number of ways to determine the location of the RF tag and/or the MU. For example, the location of the RF tag may be determined by measuring a Time Difference Of Arrival (“TDOA”) of a response signal. In particular, the location of the RF tag may be determined by comparing the time when a response signal to the RF tag arrives at three or more transceivers in different locations. The location of the RF tag may also be determined using a power measurement reading of the response signal (i.e., a Received Signal Strength Indication (“RSSI”) method). RSSI utilizes the intensity of the response signal and compares it with predetermined geographically marked points.
However, RSSI and TDOA each have different strengths and deficiencies. For example, RSSI is known to have limited accuracy in certain applications due to the dynamically changing environment (e.g., movement of objects, channel fading, etc) while TDOA may be largely affected by multipath effects (e.g., from walls and other objects in the scene). Therefore, there is a great need for an improved high-accuracy asset tracking system for locating remote or far-away assets.